Beyond the TI-84: Free Online Calculators for DIY & Construction Projects

The TI-84 is the right tool for algebra, calculus and test day — but nobody wants to hand-key a deck build into a graphing calculator at the hardware store. Weekend projects run on a different kind of math: cubic yards, waste allowances, bag counts and material costs. That math lives in free online calculators that update as you type.

Here's a practical roundup, plus the formulas behind them — the same ones you could program into your TI-84 if you really wanted to.

The workhorse: concrete volume

Pouring a patio, pad or walkway? The number that matters is cubic yards, and the formula is short:

cubic feet = length (ft) × width (ft) × [thickness (in) ÷ 12]
cubic yards = cubic feet ÷ 27

The Concrete Mix Calc runs that math for you and adds the parts people forget: bag counts (an 80-lb bag yields 0.60 ft³), the weight of the pour, the estimated cost at your local price, and the standard +10% ordering allowance for uneven subgrade and spillage.

Worked example — a 12 × 20 ft patio at 4 inches thick:

1. 12 × 20 × 0.333 = 80 ft³
2. 80 ÷ 27 = 2.96 yd³
3. Order about 3.3 yd³ with the allowance — or 147 × 80-lb bags if you're mixing by hand

The site's free concrete calculator covers the slab case in one step, and the result updates as you type, so comparing a 4-inch patio against a 6-inch driveway takes seconds.

The rest of the shed

• Gravel and stone — sold by the ton, planned in cubic yards. Rule of thumb: crushed stone runs 1.4 tons per yard, sand 1.5. Convert before you order or you'll be short a scoop.
• Paint — one gallon covers roughly 350–400 ft² per coat. Measure wall area, subtract doors and windows, multiply by coats.
• Mulch — 1 cubic yard covers about 160 ft² at 2 inches deep.
• Pavers — count = area ÷ paver area, then add 5–10% for cuts and breakage.

Each of these has a free calculator online; the pattern is always the same — length × width × depth, converted to whatever unit your supplier sells in.

Two tips that save real money

Order 10% extra. Subgrades are never perfectly even, forms flex, and some mix stays in the drum. Running short mid-pour costs far more than the spare material.

Mind the units. Thickness in inches, length in feet, delivery in yards — most project math mistakes are unit conversions, not arithmetic. Good calculators handle the conversion; a TI-84 only does what you key in.

The bottom line

Keep the TI-84 for the classroom and let purpose-built web calculators handle the garage. They're free, they work in any browser, and they speak the supplier's language — yards, bags and dollars.